1. Technical Field
The present disclosure relates to a viewing angle compensating plate and a liquid crystal display panel including the same.
2. Discussion of Related Art
Liquid crystal display devices have gained widespread acceptance in usage over cathode ray type displays. Liquid crystal display devices operate at a low voltage and consume low power, have low weight and small physical size, and operating circuits and peripheral circuits of liquid crystal display devices are relatively simple. An example of a conventional liquid crystal display apparatus is an absorptive or scattering liquid crystal display apparatus, such as a guest host liquid crystal display apparatus, polymer dispersion liquid crystal (PDLC) display apparatus or polymer stabilized cholesteric texture (PSTC) display apparatus. Another example of a conventional liquid crystal display apparatus is a polarizing liquid crystal display apparatus, such as a twisted nematic mode liquid crystal display apparatus. An absorptive or scattering liquid crystal display apparatus has a wide viewing angle, but also has a poor contrast ratio. On the other hand, a polarizing liquid crystal display apparatus has an excellent contrast ratio, but also has a narrow viewing angle. A polarizing liquid crystal display apparatus has a narrow viewing angle because the phase change of light passing through a liquid crystal layer varies depending on the direction of an optical path, and light that is not perpendicular to a polarizer is not totally extinguished while passing through an analyzing plate.
Liquid crystal display devices are commonly used as desktop monitors, and thus require a wider viewing angle. Technology such as multidomain technology, in-plane switching (IPS) technology, vertical alignment technology, optical path adjusting technology, and viewing angle compensating technology, has been developed to achieve a wider viewing angle.
In multidomain technology, one pixel is divided into a plurality of blocks, and liquid crystal molecules in each block are aligned in a different way. The average features of the blocks in the pixel represent the overall feature of the pixel, thereby improving the viewing angle. However, the process of aligning the liquid crystal molecules of each block in a different direction is complicated. Moreover, in a boundary between two blocks, alignment of liquid crystal molecules are not adjusted, resulting in leakage of light. Thus, a black matrix or a wiring of a thin film transistor is needed to block the leakage. Also, because a final viewing angle is represented as an average of viewing angles in various directions, the final viewing angle is widened in a direction that has a relatively narrow viewing angle. However, the final viewing angle is narrowed in a direction that has a relatively wide viewing angle.
In in-plane switching technology, the alignment of liquid crystal is twisted in a plane that is parallel with an alignment film by a lateral electric field, thereby widening the viewing angle. Liquid crystal display devices employing in-plane switching technology are commonly used in 17-inch desktop monitors to achieve a wider viewing angle. However, a liquid crystal display apparatus employing in-plane switching technology has a low aperture ratio, a long response time, and a relatively high operating voltage.
In vertical alignment mode technology, viewing angle is improved by using a vertical alignment agent, liquid crystal having a negative dielectric anisotropy and a phase plate. The arrangement of discotic liquid crystal in a vertical alignment mode liquid crystal display apparatus is simpler than that of a 90°-twisted nematic mode liquid crystal display apparatus. A phase plate is attached to one side of a liquid crystal layer in a vertical alignment mode liquid crystal display apparatus, whereas phase plates are formed on and beneath a liquid crystal layer in a 90°-twisted nematic mode liquid crystal display apparatus. Thus, manufacturing cost for a vertical alignment mode liquid crystal display apparatus is less than that of a 90°-twisted nematic mode liquid crystal display apparatus. The above-mentioned multidomain technology is typically employed in conjunction with vertical alignment technology.
In optical path adjustment technology, light irradiated from a backlight penetrates a liquid crystal panel in a vertical direction, and the light passing through a polarizer is scattered, thereby widening the viewing angle. Spectra view film, available from Allied Signal, Inc., may be used to scatter light that has passed through the polarizer. Generally, light is absorbed by about 10% or more when passing through an optical part. Thus, in optical path adjustment technology, transmittance of light is reduced. Moreover, patterns are formed using microlithography instead of an injection molding method, thereby increasing manufacturing cost. Light control film (LCF), manufactured by Sumitomo Chemical Company Limited, may provide a wide viewing angle by disposing diffraction gratings having various refractive indexes between a polarizer and a liquid crystal layer to adjust the degree of scattering. However, optical path adjustment technology has exhibited little effectiveness, and research of this technology is limited.
In viewing angle compensating technology, phase differences between light waves passing through a liquid crystal layer are compensated using a viewing angle compensating plate. Thicknesses of films in a conventional compensating plate differ from one another. Thus, rates of thermal expansion or contraction of the films are different, and an optical axis and a retardation value are changed due to stress differences at interfaces between the films, thus generating mottle as shown in FIG. 1.
FIG. 1 is a plan view illustrating portions of an image having mottle generated by a liquid crystal display apparatus including a conventional viewing angle compensating plate.
Referring to FIG. 1, mottle is generated in region ‘R’ of an image 1 when a conventional viewing angle compensating plate having films of different thickness is attached to a liquid crystal display apparatus. Mottle diminishes display quality of a liquid crystal display apparatus.